Cold Air Returns.........

[FinanceDude]

With regards to cold air returns in a house, what are the settings for winter and summer?I lost my scribbled notes about how to set the upper and lower grilles, and it's winter and cold, and I think they are set wrong.........

 

[thefed]

i'd guess you want to use the uppers in winter, and lowers in summer....easier to heat hot air that rose, and easier to cool cold air near the floor...thus the unit will be more efficient?


just a guess


no home i've ever been in has louvers on the cold-airs...they both stay open all the time...and i've cleaned thousands of ducts

 

[samclem]

With regards to cold air returns in a house, what are the settings for winter and summer?I lost my scribbled notes about how to set the upper and lower grilles, and it's winter and cold, and I think they are set wrong.........

I've never seen this, either. You've got adjustable louvers on the return air grills? And you adjust them differently for the different seasons? This is a new one on me.

 

[ls99]

Summer: High return, High supply. Pulls hot air from ceiling area, dumps cold air at high level.

Winter: Low return, low supply. Pulls cold air in from floor level, puts heated air at floor level, then it will rise.

This works if supply and return are well separated, say 8' or more.

Ductwork may have adjustable dampers. If so set them so more airflow goes to colder areas of house.

Hope this helps.

 

[FinanceDude]

I have louvers on the bottom grills, not the top, which are fixed. I have them in each bedroom anda couple downstairs...........

 

[ls99]

I have louvers on the bottom grills, not the top, which are fixed. I have them in each bedroom anda couple downstairs...........

I'd say open bottom louvers, use plastic film and or magnetic strips/ covers to block the top returns.

 

[samclem]

I'd say open bottom louvers, use plastic film and or magnetic strips/ covers to block the top returns.

Are we sure that deliberately blocking the fixed return grills with plastic will not starve the furnace for return air? A "Manual D" calculation would be needed in order to be sure. If the ductwork is matched to the register/grill sizes, then the effective return vent area should be larger than the supply register area--sometimes a lot larger depending on the restrictions posed by the filter.

If you inadvertently close off too many return vents, you'll reduce the efficiency of your furnace (just as a very dirty filter would). It could also damage your heat exchanger or fan motor.

 

[ls99]

Are we sure that deliberately blocking the fixed return grills with plastic will not starve the furnace for return air? A "Manual D" calculation would be needed in order to be sure. If the ductwork is matched to the register/grill sizes, then the effective return vent area should be larger than the supply register area--sometimes a lot larger depending on the restrictions posed by the filter.

If you inadvertently close off too many return vents, you'll reduce the efficiency of your furnace (just as a very dirty filter would). It could also damage your heat exchanger or fan motor.

Agree, blocking some returns would reduce airflow. OP's problem is which ones to close. I doubt he wants to mess with Manual D.

A quick test is to measure heat rise across heat exchanger with all returns open, then lower ones blocked. If heat rise does not exceed 70 degrees F, all is well. If heat rise goes to 80 or more then can't close them off.

A rash assumption on my part is that the upper and lower registers are on the same duct, or in a stud space, then change in heat rise will be somewhat higher and not significant.

OTOH I have no real idea of OP's ducting.

 

[jazz4cash]

"With regards to cold air returns in a house, what are the settings for winter and summer?I lost my scribbled notes about how to set the upper and lower grilles, and it's winter and cold, and I think they are set wrong......... "

I have louvers on the bottom grills, not the top, which are fixed. I have them in each bedroom anda couple downstairs...........

Usually only the supply grills are adjustable and the return grills are fixed. If the top grills are fixed.....what are you actually asking?

 

[FinanceDude]

"With regards to cold air returns in a house, what are the settings for winter and summer?I lost my scribbled notes about how to set the upper and lower grilles, and it's winter and cold, and I think they are set wrong......... "



Usually only the supply grills are adjustable and the return grills are fixed. If the top grills are fixed.....what are you actually asking?

What I am asking is WHEN do I close off the supply (lower) grilles?

 

[ls99]

What I am asking is WHEN do I close off the supply (lower) grilles?

Unless you have some separate heat source, such as hot water baseboard, I can't comprehend shutting of supply registers.

 

[ERD50]

FD, just to be clear - you have UPPER *and* LOWER RETURN GRILLS, right? These are grills that return air TO the furnace.

Do *both* the upper and lower have adjustment flaps to them?

I think some people are getting confused about what grills you are talking about. I think I have seen upper & lower grills with flaps, but it's rare.

If that's the case, I'm pretty sure you want to draw the cold (lower) air back to the furnace. I think 'the fed' has it backwards - it might seem 'easier' to heat the hot air, but a furnace is more efficient with a higher temperature differential, so you want to feed it cold air so that cold air can absorb more of the warm furnace. Otherwise, that heat just goes up the chimney. We don't want ot make it 'easy' on the furnace, we want it to work hard!

-ERD50

 

[FinanceDude]

FD, just to be clear - you have UPPER *and* LOWER RETURN GRILLS, right? These are grills that return air TO the furnace.
-ERD50

I don't know if I am using the term "cold air return" correctly. In each bedroom I have a vent about 7 feet off the ground, and a vent with an adjuster directly underneath it. Inside the wall is a tube/duct that I have to assume carries air back and forth in that room.

The question is: Do I CLOSE the lower vent in summer, or winter, forcing the air in that room around? Does that make sense??

 

[samclem]

I don't know if I am using the term "cold air return" correctly.

If you open all the grills/registers ad turn on the furnace, which ones does air blow out of? Those are the "supply air" registers.

The grills from which air does not blow out are called "return air" vents.

In many "regular" (low to medium-end) houses, the "return air" vents are not located in the individual rooms, they are just somewhere central (i.e. one or more in a central hallway, or just a single one at the furnace) and the builder just cuts the doors to the bedrooms abot an inch short of the floor to alow the air to leave the room and find the central return air vent. Some homes have more complex systems with return air vents in individual rooms.

The best way to know what you've got is to turn on the furnace/fan and see where the air blows out.

 

[ERD50]

In each bedroom I have a vent about 7 feet off the ground, and a vent with an adjuster directly underneath it. Inside the wall is a tube/duct that I have to assume carries air back and forth in that room.

Well, it won't carry air back *and* forth - it will do either one or the other. Either to the furnace (Return), or from the furnace (Supply)That might be adding to the confusion.

OK, so one 7' off the ground, and how far below is 'directly below', like inches below, or do you mean 'directly in line with', but two feet from the floor ? If one is directly in line with (vertically) the other, I'd assume that they are on the same duct. But, enough assuming....

As samclem is getting to - run the furnace and use a tissue paper to see which ducts are blowing out (supply), and which are sucking in (return).

The question is: Do I CLOSE the lower vent in summer, or winter, forcing the air in that room around? Does that make sense??

Depends on all of the above.

-ERD50

 

[samclem]

FD: Aren't you glad you asked this simple question?

 

[HFWR]

As a point of reference, all my return air ducts (suck) are in the walls at floor level, and all the supply vents (blow) are in the ceiling.

 

[ERD50]

FD: Aren't you glad you asked this simple question?

There's no such thing as a simple question.

And, it all depends on what you mean by "simple". You see, the answer always is: "it depends".


-ERD50

 

[ls99]

There's no such thing as a simple question.

-ERD50

To the contrary, this thread started with one.

The problem is the answer. Depending on the assumed expertise of the questioner, the answer can be one word or a novel. We have a good start on a novel.

//end thread hijack//

 

[calmloki]

Well, cold air returns here tonight according to the weatherman. Who know which way the wind blows.

I like LS99's: "A rash assumption on my part is that the upper and lower registers are on the same duct, or in a stud space, then change in heat rise will be somewhat higher and not significant".

Haven't seen that here in temperate Oregon, but the thought of putting high and low supply grills in the same stud cavity, feeding the cavity, and closing lower grill in the summer cooling season and upper grill in the winter heating season sounds pretty smart - and cheap enough to do when building.

 

[Nords]

With regards to cold air returns in a house, what are the settings for winter and summer?I lost my scribbled notes about how to set the upper and lower grilles, and it's winter and cold, and I think they are set wrong.........

When I read these "winterizing" threads, I'm amazed at the theoretical learning and practical survival skills you people have had to acquire to continue to live (and to operate your cars and your homes) through the winters.

Either that or I've lost an entire species' worth of ability to survive in a climate below tropical skin temperatures. Let me know when it's time to talk sunscreen, surf safety, and heat-stress avoidance!

 

[youbet]

FD - I have the same setup as you. For you folks without........ FD and I have cold air returns constructed so that in each room there is one at floor level and one directly above it at ceiling level. When you open the floor level damper, that closes off the duct to the upper level opening. It's one or the other.

In the winter, open the lower level (thereby closing the upper level). In the summer when the central air conditioning is running, close the lower level (thereby opening the upper level).

Our house was not built with this new fangled technology, but when we had a new HVAC system installed, they added this feature using the space between the wall studs as the ducts between the upper and lower levels. It does a nice job. Rooms have a more even temperature distribution by using the floor mounted return in the winter and the ceiling mounted return in the summer.

I thought this was much more common that it seems to be based on the comments on this thread.

 

[ERD50]

When I read these "winterizing" threads, I'm amazed at the theoretical learning and practical survival skills you people have had to acquire to continue to live (and to operate your cars and your homes) through the winters....

Six of one, half a dozen of the other: When *I* read these "termite" threads, I'm amazed at the theoretical learning and practical survival skills you people have had to acquire to continue to live through the tropics....

google "nords termites site:www.early-retirement.org" and get 48 hits!

To each his/her own. I *hate* bugs, I *hate* the idea of poison sprays in our house, I *hate* humidity and heat. I get tired of winter mid-February, but I can get out and enjoy the snow and crisp air.

-ERD50

 

[ERD50]

FD - I have the same setup as you. For you folks without........ FD and I have cold air returns constructed so that in each room there is one at floor level and one directly above it at ceiling level. When you open the floor level damper, that closes off the duct to the upper level opening. It's one or the other.

In the winter, open the lower level (thereby closing the upper level). In the summer when the central air conditioning is running, close the lower level (thereby opening the upper level).

Our house was not built with this new fangled technology, but when we had a new HVAC system installed, they added this feature using the space between the wall studs as the ducts between the upper and lower levels. It does a nice job. Rooms have a more even temperature distribution by using the floor mounted return in the winter and the ceiling mounted return in the summer.

I thought this was much more common that it seems to be based on the comments on this thread.

Interesting. I did not realize these were 'diverter' type flappers (diverting the air stream one way or the other), rather than just simple open/shut flappers.

Maybe I've just not noticed, but I do think they are pretty rare, at least in the Chicago area. I have seen them, but only a couple times that I can remember.

My (fixed - no flapper at all) returns are all mounted high, which seems odd based on your info. We use heat more than AC (and our house was built w/o AC). So I would think it would be optimized for heat, which would mean the default should be low returns.

Yes, such a simple question

-ERD50

 

[youbet]

Interesting. I did not realize these were 'diverter' type flappers (diverting the air stream one way or the other), rather than just simple open/shut flappers.

Maybe I've just not noticed, but I do think they are pretty rare, at least in the Chicago area. I have seen them, but only a couple times that I can remember.

My (fixed - no flapper at all) returns are all mounted high, which seems odd based on your info. We use heat more than AC (and our house was built w/o AC). So I would think it would be optimized for heat, which would mean the default should be low returns.

Yes, such a simple question

-ERD50

When I read your post, I was sitting at the computer in the family room at my son's house. I looked up and, sure enough, his returns are mounted high as you describe yours. Yet, at my house they were mounted low and the optional high ones were mounted at the time of a HVAC system renovation.

I did a quick google search and found this.... Note the last paragrah which seems to describe what FD and I have.

cold air return - TOH Discussions

My question is does it matter where the cold air return is located, and will it effect the heating of the house?

Yes it will.
In a heating system the cold air return should be at floor level. That's not to say in the floor but usually they will be mounted on a vertical wall at floor level.

Warm air from the heat vents will rise toward the ceiling leaving cooler air settling down toward the floor.... the law of nature. The term "cold air return" is for that reason to draw the cooler air from the floor level and return it to the furnace to be heated. If the return ducts are at ceiling level this will draw warm air returning to the furnace.

The other reason to have the cold air return vents down toward the floor level is to help with circulating the heated air coming from the warm air heat vents.
Since warm air rises you don't want all the warmth at the ceiling .... most people don't live on the ceilings .... you want it at the level of the room where you are.
This helps preventing stratification where you would have a cold zone at floor level then different layers of warmer air rising with the warmest being at the ceiling.

The cold air return at the lower point of the room will help draw the warm air down providing the heat where it's most desired.

If you will be adding air conditioning one method that's being done is adding two return air vents ... one at the floor level for heating and one at the ceiling for A/C with dampers that allow you to close off one of the ducts and open the other so that the system can work to its maximum in each season.

Hope this helps.

I also looked at some other sites and found differing opinions as to which location of return ducts makes occupants of a room feel "more comfortable" under both heating and cooling conditions. Maybe that is why my HVAC guy set me up with both??